Sixteen-year-old Markies Ross was riding with a neighbor to Central High School on Tuesday when they came upon police cars and yellow crime-scene tape. Beyond it, he caught a glimpse of a body. It looked familiar.

Markies got out of the car and asked officers if he could get closer. They wouldn’t let him. But he soon learned that what he had feared was true: His brother, 18-year-old Marckel Norman Ross, had been gunned down that morning on his way to the same Capitol Heights school.

“I can’t believe somebody would do this to him,” Markies said later. “He was a great person. . . . Everybody loved him.”

Ross, who ran track and dabbled in modeling, is the second Prince George’s County high school student shot to death less than a month into the school year. On Aug. 22, Amber Stanley, a Charles H. Flowers High School senior, was killed in her Kettering home. Prince George’s police spokeswoman Julie Parker said that although detectives have no suspects or motive in either slaying, “at this point we don’t have any reason to believe there is a connection between the cases.”

Still, Earnest L. Moore, president of the Prince George’s County PTA Council, said that the slayings have left some parents on edge.

“Parents are afraid,” he said.

Marckel Ross left his home on Abel Avenue in Capitol Heights about 6:30 a.m., his mother last joking with her son to “get out” of her room as his sister helped him button a shirt sleeve, family members said. About halfway through his roughly 1.5-mile walk, the teen was killed.

“We don’t have a clue,” Elizabeth Ross said of her son’s slaying. “He was a very bright child. . . . Marckel didn’t bother nobody.”

Shortly before 7 a.m., Parker said, several 911 calls came in about a “man down” on Old Central Avenue, and responding officers found Ross’s body.

Parker said investigators believe that Ross, who was carrying schoolbooks, was taking his usual route to Central High, where he was in the 11th grade. He was believed to have been walking alone, and police were searching for witnesses Tuesday evening.

On Tuesday, investigators descended on the school to interview students while police cadets combed the crime scene on hands and knees. Some parents, too, went to the school, concerned for their own children’s safety.

“Just walking to school — how does that happen?” said Anthony Smith, whose son, Denote, is in the ninth grade. “That’s very terrifying for people who have their kids walking.”

The scene in Capitol Heights where an 18-year-old high school student was shot and killed Tuesday morning. (Matt Zapotosky/The Washington Post)

Another parent, Dawn Peacher, said she worried about violence spilling into the school.

“I don’t feel like she’s safe coming to school here with that going on,” Peacher said of her daughter, Janay.

Ross said her son had not complained of any disputes with anyone at Central, although he had struggled with classes and bullying when he first moved to Prince George’s from Anne Arundel County in 2009. Last year, she said, he got into several fights with other students, but she added that she believed that the problems were long settled.

Charoscar Coleman, Central High’s principal, said that Ross was a “strong student” who had participated in a school modeling program called Showtime Couture. He said that grief counselors were at the school on Tuesday to help calm a student body that was “trying to deal with the emotion of the moment.”

“He was beloved, and we’re going to miss him greatly,” Coleman said. “This was a young man who deserved to live.”

Even as police probed Ross’s slaying, detectives continued to delve into who could have wanted to shoot Stanley, 17, a well-liked student who aspired to go to Harvard and worked as a model. On Monday, in front of hundreds of residents at a community meeting in Kettering, police officials pleaded for tips from the public, announcing that an entire homicide squad had been dedicated to investigating the baffling crime.

Parker said that although no motive has been determined, the investigation was in its early stages.

Ross said that she sometimes worried about her son’s long walk to school and encouraged him to ride with the neighbor who drove her younger children, Markies and his 14-year-old brother, Marquale. But the 18-year-old was too outgoing to heed her advice, family members said.

“I always feel like that was too far for him to be walking,” Ross said.

Outside Ross’s home Tuesday, family members hugged one another and shared pictures of the young man pulled from Facebook, Instagram and Twitter.

Norman Thompson, Marckel’s father, said his son ran track, worked with an ROTC program and participated in the school modeling group. Ross was “always smiling,” his father said, and was known among family members for his dancing ability and love of fashion.

Although he did not know what he wanted to do in life, he had been talking with family members about joining the military, becoming a police officer or going to college, his mother said. She said she last saw him just before he left for school, jokingly telling him “Get out of my room” because her son had directed the same phrase at her the night before.

“I’m gonna miss his smile. I’m gonna miss his dancing,” Ross said. “Marckel was a good son. He was a good child.”